Process and apparatus for melt spinning thermoplastic yarn



H. W. HEMKER ETAL PROCESS AND APPARATUS FOR MELT SPINNING THERMOPLASTIC .YARN

Filed Jan. 4, 1968 United States Patent 3,497,586 PROCESS AND APPARATUS FDR MELT SPINNING THERMOPLASTIC YARN Herman W. Hemker, West Chester, and Arlen K. Sarian,

Havertown, Pa., assignors to FMC Corporation, Philadelphia, Pa., a corporation of Delaware Filed Jan. 4, 1968, Ser. No. 695,711 Int. Cl. D01d /08 US. Cl. 264-237 Claims ABSTRACT OF THE DISCLOSURE A method and apparatus for melt spinning thermoplastic polymer filaments and yarn of improved uniformity is disclosed herein. More particularly, it includes the stabilization of the molten filaments during their cooling by steadying the filaments with a cushion of a steady current of a gaseous medium.

It is known to guide or forward thread with air guides to prevent degradation of the fine denier thread by rubbing against a solid surface. This is shown, for example, in US. Patent No. 2,191,791. It is also known to stabilize melt spun filaments which have been subjected to air turbulence in the quenching process utilizing a subsequent horizontal air current prior to the filaments being directed over a guide means. This is shown in US. Patent No. 3,067,458.

Air turbulence in the neighborhood of extruded molten polymeric filaments is generally present with the use of any type of gaseous quenching device for a multiplicity of spun filaments and is known to be detrimental to the uniformity of the filaments and subsequent fiber characteristics. Of particular importance in this respect is the dyeing uniformity of the resulting fiber.

It has now been found that air turbulence which occurs during the quenching of molten filaments can be minimized and the molten filaments steadied during the quenching period by the use of a cushion of a gaseous medium emanating from a relatively narrow source positioned against the filament stream or path below the quenching area.

Thus, it is a principal object of this invention to provide a method and apparatus for the preparation of melt spun fibers having improved uniformity.

It is another object of this invention to provide a method and apparatus wherein melt spun filaments can be guided at a point closer to the spinneret from which said filaments originate than that which is feasible using conventional solid guide means.

These and other objects are accomplished in accordance with this invention which comprises extruding a plurality of molten synthetic polymer filaments downwardly into a cooling gaseous medium, substantially solidifying the filaments, then directing a cushion of a steady current of a gaseous medium against said filaments, said current emanating from a relatively narrow source positioned in the filament stream and substantially perpendicular thereto, said current having sufiicient force to prevent contact of said filaments with the current source.

The invention also includes an apparatus combination which comprises an apparatus for melt extruding filamentforming polymer including a multi-orifice spinneret, means adjacent the spinneret to direct a cooling current of a gaseous medium against spun molten filaments, and means adapted to emit a steady cushion of a gaseous medium positioned below the cooling means in the path of molten filaments originating from said spinneret.

The method and apparatus of this invention will be more fully understood on reference to the accompanying drawing in which:

FIG. 1 is a schematic side view of one modification of this invention;

FIG. 2 is a schematic side view of another modification of this invention;

FIG. 3 is a schematic side view of still another modification of this invention;

FIG. 4 is a perspective view of a quenching apparatus which is advantageously used for this invention;

FIG. 5 is a perspective view of a gas cushion supply means for this invention; and

FIG. 6 is a perspective view of a modified gas cushion supply means for this invention.

In FIG. 1, a plurality of molten filaments represented by numeral 1 are extruded downwardly from spinneret 2 into and through a cooling gaseous medium such as a horizontal air stream represented by arrows 3. Ordinarily, the passage of cooling air is deflected around the filaments and the greater the number of extruded filaments, the more the air is deflected to produce undesirable turbulence. This turbulence causes the molten filaments to waiver or quiver in their downward path and this, in turn, increases non-uniformity in the individual filament denier and dyeability.

At a distance below the point at which the filaments are substantially solidified, although they may still be tacky or soft, gas cushion source or supply means 4 is positioned in the path or stream of the filaments 1. The filament bundle, as it passes in the vicinity of the gas or air cushion, represented by arrows 5, generally flattens to conform to the air source or supply means 4, but does not touch the surface thereof. After passing gas cushion 5, the filaments may travel over a guide or other fiber advancing means (not shown), or be taken up directly, usually after passage through chimney or tube 6.

FIG. 2 demonstrates a modification of this invention wherein two gas cushion sources 7 and 8, from which gas cushions 9 and 10 emanate, are positioned in the path of the filaments 1 to provide additional control of the filament bundle. It will be realized that the gas cushions need not be directly opposite one another as shown, but can be positioned above and below one another. It should also be realized that more than two gas cushions can be used in various positions to stabilize and guide the filaments along a desired path.

In FIG. 3, gas cushion 12 from source 11 acts both to stabilize filaments 1 and as a guide means whereby the filaments are caused to change direction.

FIG. 4 represents an improved quenching apparatus which is more particularly described and claimed in copending US. patent application Ser. No. 695,604, filed of even date herewith by Arlen K. Sarian. This quenching apparatus may be advantageously used in conjunction with the method and apparatus of this invention, since it permits cooling of the molten filaments as close up to "a circular spinneret assembly as possible while facilitating access to the spinneret face for cleaning and lacing up. The quenching apparatus generally comprises an enclosure '13 adapted to receive a cooling air supply and having a longitudinally concave foraminous front surface 14 extending into the enclosure. The edges of the walls of the enclosure conform to the edges of the foraminous front surface thereby forming a semicylindrical quenching channel through which the molten filaments pass. A cooling gas inlet conduit =15, which is adapted to receive gas from a connecting supply (not shown), is attached to the back of enclosure 13. Advantageously, the enclosure 13 can contain an internally positioned perforated screen (not shown) to more effectively distribute cooling gas flow.

This quenching device provides a semi-circular distribution of a horizontal quenching gas flow without necessitating a concurrent fiow as produced with completely cylindrical quenching means. T he device can also be pushed back away from the spinneret without having molten polymer drip over it, and it can be easily adjustably positioned with respect to its distance from the extruded filaments.

FIG. is an enlarged perspective view of, what is termed for the purpose of this invention, the gaseous medium source. In this embodiment, the source comprises a metallic tube 16 having one closed end 17 and a microporous body 18 which is composed of a sintered metal which permits the passage of a cushion of gas, such as air, through its pores when gas under pressure is supplied through flexible tube As a practical matter, cylindrical tubes having a diameter of at least about A of an inch and ranging up to 2 or 3 inches will be most useful for this invention.

FIG 6 is an alternate embodiment of a source for a gas cushion comprising an arcuate tube 20 of a microporous metal as described for FIG. 5. Two of these arcuate tubes 20 can be used to provide a completely circular gas cushion and guide, if desired.

The method and apparatus of this invention are useful for the preparation of fibers from synthetic filament-forming thermoplastic resin including, for example, polester resin, e.-g. polyethylene terephthalate; isotactic polypropylene resin, polyamide resin, e.g. polyhex'a methylene adipamide and polycaprolact-am, polyvinyl chloride resin, polycarbonate resin, polyphenylene oxide resins and the like, as well as mixtures of such resins.

The method and apparatus of this invention have distinct advantages over prior art methods. The gas cushion of the invention can be readily moved to any desired location along the path of the falling filaments. It can be moved much closer up to the quench zone than conventional guide means to stabilize, guide and even further cool the spun filaments. Conditions which vary with the spinning of different polymers are much more readily accommodated with the apparatus and method disclosed herein.

To demonstrate the improvement in uniformity of fibers produced in accordance with this invention, filament-forming isotactic polypropylene resin was melt extruded at 250 C. through a circular spinneret assembly having 68 holes. The filaments were quenched with cooling air having a velocity measured at the straight quench screen of about 110 feet per minute and taken up at a speed of 200 meters per minute. The spun, undrawn yarn had a total denier of 3800.

The method of this invention was used in the above procedure to spin a portion of the yarn while a control yarn was spun without the gas cushion. In this spinning operation, a gas cushion source, which was about a 1% inch diameter microporous metal tube, was placed horizontally across the path of the filaments about 66 inches down from the spinneret assembly. Air was fed to the metal tube under a line pressure of about p.s.i.g. to create a cushion of air at the surface of the tube sufficient to cause the filament bundle to flatten out and to prevent the filaments from contacting the surface of the tubefIhe yarn, in both cases, was taken up by first passing it over a finish roll, around two godets and winding on a spool.

The yarn samples were tested for non unifor-mity by following the general procedures of ASTM-1425, Method of Test for Unevenness of Textile Strands, using an instrument of the type which measures directly the properties of the yarn which change the capacity of a condenser when the yarn passes between its plates. The lower the value obtained in this test procedure, the more uniform is the filamentary product. Yarn which was spun in the above manner without utilizing the gas cushion of this invention, produced -a nonuni-formity value in the est procedure of 4. 1, while yarn spun in the same manner utilizing the gas cushion as described produced a non-uniformity value of only 1.9. It is seen, therefore, that the method and apparatus of this invention will produce a significant decrease in yarn non-uniformity.

Various changes and modifications may be made practicing this invention without departing from the spirit and scope thereof, and therefore, the invention is not to be limited, except as defined in the appended claims.

We claim:

1. A method comprising extruding a plurality of molten synthetic polymer filaments downwardly into a cooling gaseous medium, solidifying the filaments, then directing a cushion of a steady current of a gaseous medium against said filament, said current emanating from a relatively narrow source positioned in the filament path and substantially perpendicular thereto, said current having sufiicient force to prevent contact of said filaments with the current source, and forwarding the plurality of filaments.

2. The method of claim 1 wherein the cooling gaseous medium is directed radially inwardly and horizontally across the molten filaments over an arc of about 3. The method of calim 1 wherein at least one other cushion of a steady current of a gaseous medium is directed against the filaments at a position no farther up the filament path than the gaseous cushion of claim. 1.

4. The method of claim 1 wherein the direction of the filament path is changed at said cushion of the gaseous medium.

5. The method of claim 1 wherein the synthetic polymer filaments contain a substantially isotactic polymer of propylene.

6. The method of claim 1 wherein the synthetic polymer filaments contain polyethylene terephthalate resin.

7. An apparatus comprising means to extrude downwardly a plurality of molten synthetic polymer filaments from a multi-orifice spinneret assembly, gaseous cooling means for said molten filaments adjacent said spinneret, and filament steadying means positioned below said cooling means in the path of the solidified filaments, said steadying means comprising a relatively narrow element positioned substantially perpendicularly to the falling filaments and having means to emit a cushion of a steady current of a gaseous medium with sufiicient force to prevent the filaments from touching said element.

8. The apparatus of claim 7 wherein said spinneret as sembly is circular and said gaseous cooling means comprises walls defining an enclosure adapted to receive a cooling gaseous medium, said walls including a front wall having a longitudinally concave foraminous surface extending into said enclosure, said enclosure walls having edges substantially coextensive with the edges of concave surface whereby said gaseous cooling means cooperates with said spinneret assembly and partially surrounds the extruded molten filaments, and said enclosure having inlet means for a supply of said cooling gaseous medium.

9. The apparatus of claim 7 wherein said steadying means comprises a closed tube having means to receive a pressurized gas and at least a portion of said tube comprising a microporous section from which a cushion of a steady current of the pressurized gas will emanate.

10. The apparatus of claim 9 wherein said steadying means comprises a straight metallic tube closed at one end 6 and adapted to receive pressurized gas at the other end, at 3,338,992 8/ 1967 Kinney.

least a portion of the surface of said tube being porous. 3,379,811 4/ 1968 Hartmann et a1.

3,423,266 1/1969 Davies et a1. References Cited UNITED STATES PATENTS 5 FROME, Primary Examiner 2 32 42 4 195 Lennox I. H. WOO, Assistant Examiner 3,266,969 8/1966 Makansi. 3,320,343 5/1967 Buschmann et al. US CL 3,325,906 6/1967 Franke. 18-8;264176,210 

